They only cover 2% of the Earth’s surface, but cities are big contributors to the climate crisis, a new study showed Monday.
Megacities in Asia, including Shanghai in China and Tokyo in Japan, were especially important emitters. Yet cities in Europe, Australia and the U.S. had significantly higher per capita emissions than cities in developing areas, with stationary energy, also known as electricity generation and fuel combustion
and transportation the two main contributors of emissions.
The findings, published in the journal Frontiers in Sustainable Cities, present what researchers claim is the first global balance sheet of greenhouse gasses (GHGs) emitted by major cities around the world.
“Nowadays, more than 50% of the global population resides in cities,” said co-author Dr. Shaoqing Chen, of Sun Yat-sen University, China. All “cities are reported to be responsible for more than 70% of GHG emissions, and they share a big responsibility for the decarbonization of the global economy. “
The study’s aim was to research and monitor the effectiveness of historical GHG reduction policies implemented by 167 globally distributed cities that are at different developmental stages.
U.S. cities aren’t great at measuring how much pollution they emit and not just by a small margin — the average underreporting error is over 18%, a separate study showed.
Cleveland was one sizeable city called out in the report for greenhouse gas measurements that are off by 90%. But city calculations missed the researchers’ count in the other direction as well: tech hub Palo Alto, Calif., may be overreporting emissions by 42%.
China, classified in this report as a developing country, also had several cities where per capita emissions matched those of developed countries. It is important to note that many developed countries outsource high carbon production chains to China, which increases export-related emissions for the latter.
Chinese coal consumption is poised to hit a record this year, according to the International Energy Agency, a closely watched global tracking organization, a bump up that contradicts the view held by many climate change and energy experts that coal burning in the world’s second-biggest economy and largest polluter had peaked.
President Xi Jinping told the U.S.-led Climate Leaders’ Summit in April that China vows to start phasing down coal consumption from the 2026-2030 period as part of its efforts to reduce greenhouse gas emissions.
In 2015, 170 countries adopted the nonbinding Paris climate agreement, with the goal limiting the average global temperature increase to 1.5°C. Many countries and cities proposed targets for greenhouse gas mitigation toward that goal. But U.N. data suggests that without stricter actions to mitigate the climate crisis, Earth is heading for a temperature increase of more than 3°C by the end of the 21st century.
“Current inventory methods used by cities vary globally, making it hard to assess and compare the progress of emission mitigation over time and space,” said Chen.
The researchers suggest three considerations for cities in lowering their emissions:
First, key emitting sectors should be identified and targeted for more effective mitigation strategies. For example, the differences in the roles that stationary energy use, transportation, household energy use, and waste treatments play for cities should be assessed.
Second, development of methodologically consistent global GHG emission inventories is also needed, to track the effectiveness of urban GHG reductions policies.
And finally, cities should set more ambitious and easily-traceable mitigation goals. At a certain stage, carbon intensity is a useful indicator showing the decarbonization of the economy and provides better flexibility for cities of fast economic growth and increase in emission. But in the long run, switching from intensity mitigation targets to absolute mitigation targets is essential to achieve global carbon neutrality by 2050.
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